If su is compiled with PAM support, it is possible for any local user
to send SIGKILL to other processes with root privileges. There are
only two conditions. First, the user must be able to perform su with
a successful login. This does NOT have to be the root user, even using
su with the same id is enough, e.g. "su $(whoami)". Second, SIGKILL
can only be sent to processes which were executed after the su process.
It is not possible to send SIGKILL to processes which were already
running. I consider this as a security vulnerability, because I was
able to write a proof of concept which unlocked a screen saver of
another user this way.
Some of the supplied tools use functions which are not signal-safe.
Most of the times it's exit() vs. _exit().
In other times it's how the standard output or standard error is
handled. FILE-related functions shall be avoided, therefore I replaced
them with write().
Also there is no need to call closelog(). At worst, it allows to
trigger a deadlock by issuing different signal types at bad timings.
But as these fixes are about race conditions, expect bad timings in
general for these bugs to be triggered. :)
* src/su.c: Terminate the child (if needed) before closing the PAM
session. This is probably more correct, and avoid reporting
termination from signals possibly sent by PAM modules (e.g. former
versions of pam_systemd). Debian#670132
* src/su.c: When a SIGTSTP is caught, reset caught to 0. There is
no need to kill the child in such case after su is resumed. This
remove the "Session terminated, terminating shell...
...terminated." messages in such case.
save_caller_context() is allocated and freed.
* src/su.c: Added missing #endif indication
* src/su.c save_caller_context(): password only needed if
SU_ACCESS and !USE_PAM.
* src/su.c: Added function prototypes.
* src/su.c: Rename shellstr parameter to shellname to avoid
collision with static variable.
* NEWS, src/su.c: Added support for PAM modules which change
PAM_USER.
child and listening for signal in the parent from run_shell().
prepare_pam_close_session() is now executed before the creation of
the pam session and before the UID is changed. This allows to
close the session as root.
use the pwent global variable to communicate between APIs of
different files. Added boolean parameter su_to_root to
check_su_auth().
* src/su.c (check_perms): Return the passwd entry of the finally
authenticated user. Remove usage of the pwent variable.
* src/su.c: The password of the caller is the one from the
spwd structure only if the passwd's password is 'x'.
after the switch to the final subsystem. The previous architecture
forced to always change the environment (the shell starts with a
'*' and was thus restricted, and change_environment could not be
reset to false).
definition of shellstr, PATH and IFS is not influenced (getenv,
getdef, restricted_shell) by and does not influence (addenv does
not change environ) the authentication. And the authentication
does not overwrite those definitions. This will ease an extraction
from the big main() function.
commands executed with -c. This prevents tty hijacking which could
lead to execution with the caller's privileges. This required to
forward signals from the terminal (SIGINT, SIGQUIT, SIGTSTP) to
the executed command.
boolean.
* libmisc/basename.c: Avoid implicit conversion of pointer to
boolean.
* libmisc/basename.c, lib/prototypes.h (Basename): Return a
constant string.
* libmisc/basename.c, libmisc/obscure.c, lib/prototypes.h,
libmisc/xmalloc.c, libmisc/getdate.h, libmisc/system.c,
libmisc/getgr_nam_gid.c, libmisc/failure.c, libmisc/valid.c: Add
splint annotations.
* libmisc/chowndir.c: Avoid memory leak.
* libmisc/chowndir.c: Do not check *printf/*puts return value.
* libmisc/chowntty.c: Avoid implicit conversion between integer
types.
* libmisc/obscure.c: Return a bool when possible instead of int.
* libmisc/shell.c: Do not check *printf/*puts return value.
* libmisc/shell.c: Do not check execle return value.
* libmisc/setupenv.c: Avoid implicit conversion between integer
types.
* libmisc/xmalloc.c: size should not be zero to avoid returning
NULL pointers.
* libmisc/hushed.c: Do not check *printf/*puts return value.
* libmisc/system.c: Avoid implicit conversion of integer to
boolean. safe_system last argument is a boolean.
* libmisc/system.c: Check return value of dup2.
* libmisc/system.c: Do not check *printf/*puts return value.
* libmisc/system.c: Do not check execve return value.
* libmisc/salt.c: Do not check *printf/*puts return value.
* libmisc/loginprompt.c: Do not check gethostname return value.
* libmisc/find_new_gid.c, libmisc/find_new_uid.c: Do not check
gr_rewind/pw_rewind return value.
* libmisc/ttytype.c: Limit the number of parsed characters in the
sscanf format.
* libmisc/ttytype.c: Test if a type was really read.
* libmisc/sub.c: Do not check *printf/*puts return value.
* libmisc/sub.c: Avoid implicit conversion of integer to boolean.
* src/userdel.c: Fix typo in comment.
* src/userdel.c: Avoid implicit conversion of boolean to integer.
* src/userdel.c: safe_system last argument is a boolean.
* src/newusers.c: Avoid implicit conversion of boolean to integer.
* src/newusers.c: Avoid implicit conversion of integer to boolean.
* src/usermod.c: Add brackets.
* src/usermod.c: Avoid implicit conversion of characters or
integers to booleans.
* src/vipw.c: Avoid implicit conversion of integer to boolean.
* src/su.c: Avoid implicit conversion of integer to boolean.
* src/su.c: Add brackets.
* src/useradd.c: Avoid implicit conversion of characters or
integers to booleans.
instead of an int.
* libmisc/obscure.c, libmisc/tz.c, src/passwd.c, lib/encrypt.c,
libmisc/copydir.c, lib/prototypes.h: Add splint annotations.
* libmisc/tz.c: Fix some const issues.
* libmisc/tz.c: Avoid multi-statements lines.
* libmisc/tz.c: Add brackets.
* libmisc/copydir.c: Do not check *printf/*puts return value.
* libmisc/copydir.c: Fail if we cannot set or reset the SELinux
fscreate context.
* libmisc/copydir.c: Use xmalloc instead of malloc.
* libmisc/copydir.c: Do not check lutimes return value
* src/vipw.c: Avoid implicit conversion of integer to boolean.
* src/su.c (iswheel): Return a bool instead of an int.
* src/passwd.c: Remove insert_crypt_passwd(). Use xstrdup instead.
* src/passwd.c: Return constant strings when sufficient.
* src/passwd.c: Do not check *printf/*puts return value.
* src/passwd.c: Avoid implicit conversion of character to boolean.
* src/passwd.c: Do not check sleep return value.
* src/sulogin.c: Do not check *printf/*puts return value.
* lib/encrypt.c: Do not check fprintf return value.
